Electric machines such as electric motors, active magnetic bearings or electromagnetic sensors are sometimes used in harsh environment. Corrosion due to presence of sulphide, water, mercury, hydrocarbons in upstream gas may occur on lamination stacks of either a rotor or a stator of an electric machine. Such laminations may be made of ferromagnetic material (Si-Iron, Co-Iron, Ni-Iron . . . ). It is therefore necessary to form a protective layer between a lamination stack and a severe environment.
Furthermore scratches may occur during handling of the elements of the electric machine. If such scratches are made on sensor's lamination rotor stacks, rotating harmonics are created and picked up by the sensor. It results in disturbance of all the control of an associated electric machine.
It is therefore desirable that a rotor's stack of laminations be hardened and better protected to diminish harmonic amplitude or even avoid harmonics (case of very low impact of mechanical scratch on the lamination stack).
To avoid problems caused by harsh environment it has been envisaged to use an anti-corrosive painting. However, tests have demonstrated that there is a lack of paint adhesion when such anti-corrosive painting is used on a rotor and the rotor is spinning at high rotation levels.
Patent document CA 2624347 A1 relates to a rotor shaft assembly for magnetic bearing for use in corrosive environment. The rotor shaft is formed of parts of a ferromagnetic material comprising a plurality of ferromagnetic rotor laminations disposed on the rotor shaft. A barrier layer, by anti-corrosive paint, is formed on selected exposed surfaces of the rotor shaft and is effective to resist corrosion. The barrier layer is formed of a material selected from the group consisting of epoxies (filled epoxies, filled silicones . . . ), fluoropolymer (PFA, ETFE, ECTFE, PTFE, PFA, FEP, MFA, PVDF . . . ), oxide conversion material, phosphate conversion material, chromate conversion material, a di (4-hydroxyphenol) isopropylidene diglcycidyl ether-di (4-hydroxyphenol) isopropylidene copolymer. The barrier is applied at room temperature with a brush or a spray. The adherence of the barrier strongly depends on the surface preparation of the surface of the laminations. Such deposition method induces that thickness of the barrier layer is relatively thick: indeed, this thickness is comprised between 178 μm and 406 μm. In practice, experiments have demonstrated that coating tend to be damaged when rotor is spinning at high speeds level.
It is therefore an object of the present invention to improve the protection of all ferromagnetic lamination stacks (rotor and stator parts) of an electric machine, especially an active magnetic bearing, when the electromagnetic components are in contact with a sour environment. Moreover, coating material and coating method are intended to prevent drawbacks especially when the rotor is spinning at high speed.